PROCESS FOR CONVERTING PLASTICS

Description

FIELD

The field is the recycling of plastic materials. Particularly, the field relates to recycling of a variety plastic materials to produce pyrolysis product.

BACKGROUND

Recycling is the process of collecting and processing materials from waste streams that would otherwise be disposed of as trash and turning them into new products. Recycling has benefits for communities and for the environment, since it reduces the amount of waste sent to landfills, conserves natural resources such as timber, water, and minerals, increases economic security by tapping a domestic source of materials, prevents pollution by reducing the need to collect new raw materials, and saves energy. After collection, recyclables may be sent to a material recovery facility (“MRF”) to be sorted, cleaned, and processed into useable materials.

The recovery and recycling of waste plastics is held with deep interest by the general public which has been participating in the front end of the process for decades. Past plastic recycling paradigms can be described as mechanical recycling. Mechanical recycling entails sorting, washing and melting recyclable plastic articles into molten plastic materials to be remolded into a new clean article. However, this mechanical recycling process has its limitations including the types and formats of the plastics that can be used and the degradation of the material after each recycle. Collection of recyclable plastic articles at materials recovery facilities inevitably includes non-plastic articles that have to be separated from the recyclable plastic articles. Similarly, collected articles of different plastics have to be separated from each other before undergoing melting because the articles molded of different plastics would not typically have the quality as an article molded of the same plastic. Sorting of collected plastic articles from non-plastic articles and then into like plastics adds expense to the process that reduces its economic efficiency. Additionally, recyclable plastic articles have to be properly cleaned to remove non-plastic residues before melting and remolding which additionally increases the expense of the process. The recovered plastic also does not possess the quality of virgin grade plastic resins. The economics of the plastic recycling process and the lower quality of recycled plastic have prevented widespread acceptance of this renewable resource.

Municipal Solid Waste (“MSW”) is a broad term for waste streams that cover household, commercial, and industrial sources. Within each of these categories, there are thousands of different materials and products.

Currently, only some plastics are recyclable. Recycling rates also vary between types of plastic. Several types are in common use, each having distinct chemical and physical properties. This leads to differences in the ease with which they can be sorted and reprocessed, which affects the value and market size for recovered materials. Plastic packaging and products that are made from a single material (e.g., polyethylene terephthalate (“PET”), high density polyethylene (“HDPE”), and polypropylene (“PP”)) can be more easily recycled. Plastics that are sometimes or almost never recyclable include polyvinyl chloride (“PVC”), low density polyethylene (“LDPE”), linear low-density polyethylene (“LLDPE”), and polystyrene (“PS”). Additionally, plastic can only be recycled a limited number of times

Plastic waste may be simply burnt as part of refuse-derived fuel (“RDF”) in a waste-to-energy process, or it may be first chemically converted to a synthetic fuel. Mixed plastic waste can be depolymerized to provide a synthetic fuel. This synthetic fuel has a higher heating value than the starting plastic and can be burnt more efficiently, although it remains less efficient than fossil fuels.

A paradigm shift has enabled the chemical industry to rapidly respond with new chemical recycling processes for waste plastics. The new paradigm is to chemically convert the recyclable plastics in a pyrolysis process operated at about 350 to 600° C. to liquids. The liquids can be refined in a refinery to fuels, petrochemicals and even monomers that can be re-polymerized to make virgin plastic resins. The pyrolysis process still requires separation of collected non-plastic materials from plastic materials fed to the process, but cleaning and perhaps sorting of plastic materials may not be as critical in chemical recycling.

Higher temperature pyrolysis is under investigation and is viewed as a route to convert plastics directly to valuable products without further refining. Conversion of mixed plastics presents a circular way of recycling a renewable resource that as of yet has not been fully economically developed. What is needed is a viable process to convert mixed plastics into valuable products.

BRIEF SUMMARY

A process for converting plastics is disclosed. The process comprises pyrolyzing a plastic feed stream in a first pyrolysis reactor to produce a pyrolysis vapor stream. The pyrolysis vapor stream is pyrolyzed in a second pyrolysis reactor to produce a pyrolysis product stream. The first pyrolysis reactor may be operated at a higher temperature than the second pyrolysis reactor. The plastic feed stream may be separated from a mixed-plastic stream. The present process comprises sorting the plastic into multiple plastic feed streams based on the contaminant level that may be present in the stream. The sorted multiple plastic feed streams are processed in dedicated reactors suitable for handling the contaminants level in the feed stream. This way the sorting capital cost is reduced, yield is improved, and the waste from pre-treatment of the mixed-plastic stream can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a process for converting plastics in accordance with an exemplary embodiment of the present disclosure.

FIG. 2 is a schematic drawing of a process for converting plastics in accordance with another exemplary embodiment of the present disclosure.

DEFINITIONS

The term “communication” means that fluid flow is operatively permitted between enumerated components, which may be characterized as “fluid communication”.

The term “downstream communication” means that at least a portion of fluid flowing to the subject in downstream communication may operatively flow from the object with which it fluidly communicates.

The term “upstream communication” means that at least a portion of the fluid flowing from the subject in upstream communication may operatively flow to the object with which it fluidly communicates.

The term “direct communication” means that fluid flow from the upstream component enters the downstream component without passing through any other intervening vessel.

The term “indirect communication” means that fluid flow from the upstream component enters the downstream component after passing through an intervening vessel.

The term “bypass” means that the object is out of downstream communication with a bypassing subject at least to the extent of bypassing.

The term “predominant”, “predominance” or “predominate” means greater than 50%, suitably greater than 75% and preferably greater than 90%.

The term “carbon-to-gas mole ratio” means the ratio of mole rate of carbon atoms in the plastic feed stream to the mole rate of gas in the diluent gas stream. For a batch process, the carbon-to-gas mole ratio is the ratio of moles of carbon atoms in the plastic in the reactor to the moles of gas added to the reactor.

DETAILED DESCRIPTION

FIG. 1 shows an embodiment of a process for converting plastics 101. A mixed-plastic stream in line 102 may be processed and converted in the process 101. In an aspect, mixed-plastic stream in line 102 may be taken from municipal solid waste (“MSW”). The mixed-plastic stream in line 102 may be charged to a pretreatment section 110 to separate waste material and contaminants from the plastic. The pretreatment section 110 may include sorting the plastic into a desired plastic and a non-desired plastic.

Plastic pieces in MSW can be composed of one or more organic polymers, one or more inorganic materials, and come in many different colors, shapes, and sizes. Examples of these plastics include potato chip bags, squeezable juice boxes, select drink containers, and electronics electromagnetic sensitive packaging.

MSW may contain a wide variety of waste or discarded material. For instance, the waste material may include biodegradable waste, non-biodegradable waste, ferrous materials, non-ferrous metals, paper or cardboard in various forms, plastic (some of which may contain trace toxic metals that were used as catalysts, stabilizers or other additives), paints, varnishes and solvents, fabrics, wood products, glass, chemicals including medicines, pesticides and the like, solid waste of various types and a wide range of other materials. The waste material includes household waste material and industrial waste material, the latter preferably being so-called “safe” industrial waste; that is, low in toxic or hazardous materials.

The mixed-plastic stream in line 102 may include thermoplastic materials. Thermoplastic can be categorized in four types of plastics.

Standard plastics or commodities: plastics manufactured and used in large quantities due to their price and good characteristics in many ways. Some examples are polyethylene (“PE”), polypropylene (“PP”), polystyrene (“PS”), polyvinyl chloride (“PVC”), or the copolymer acrylonitrile butadiene styrene (“ABS”).

Engineering plastics: used when good structural, transparency, self-lubrication, and thermal properties are needed. Some examples are polyamide (“PA”), polyacetal (“POM”), polycarbonate (“PC”), polyethylene terephthalate (“PET”), polyphenylene ether (“PPE”), and polybutylene terephthalate (“PBT”).

Special plastics: they have a specific property to an extraordinary degree, such as polymethyl methacrylate (“PMMA”), which has high transparency and light stability, or polytetrafluoroethylene (Teflon), which has good resistance to temperature and chemical products.

High-performance plastics: mostly thermoplastic with high heat resistance. In other words, they have good mechanical resistance to high temperatures, particularly up to 150° C. Polyimide (“PI”), polysulfone (“PSU”), polyethersulfone (“PES”), polyarylsulfone (“PAS”), polyphenylene sulfide (“PPS”), and liquid crystal polymers (“LCP”) are high-performance plastics.

Many plastic items bear symbols identifying the type of polymer from which they are made. These resin identification codes, often abbreviated RICs, are used internationally. There are seven codes in all, six for the most common commodity plastics types and one as a catch-all for everything else. These types are also be referred to herein as the polymer type #1 to type #7. Polymer type #1 refers to polyethylene terephthalate (“PET”), type #2 refers to high-density polyethylene (“HDPE”), type #3 refers to polyvinylchloride (“PVC”), type #4 refers to low-density polyethylene (“LDPE”), type #5 refers to polypropylene (“PP”), type #6 refers to polystyrene (“PS”), and type #7 refers to other polymers not in polymer types #1 to #6 such as acrylic, polycarbonate (“PC”), polyactic fibers, polylactide, nylon, fiberglass, ABS.

In an aspect, the pretreatment section 110 may separate the mixed-plastic stream in line 102 into separate groups by physically depositing such as diverting or ejecting the material pieces into separate receptacles or bins. The material pieces may be sorted into separate bins in order to separate material pieces having physical characteristics that are distinguishable from the physical characteristics of other material pieces such as visually discernible characteristics or features, different chemical signatures, etc. The pretreatment section 110 may comprise a conveyor system to convey one or more plastic streams 102 which sorts the plastic into predetermined desired plastic groups.

In an embodiment, the mixed-plastic stream in line 102 may be obtained from a materials recycling facility (MRF) that is otherwise sent to a landfill.

In an embodiment, the mixed-plastic stream in line 102 may comprise refuse-derived fuel (“RDF”). Refuse-derived fuel (RDF) or solid/specified recovered fuel (SRF) is a fuel produced by shredding and dehydrating MSW. RDF consists largely of combustible components of municipal waste such as plastics and biodegradable waste. RDF processing facilities are normally located near a source of MSW and, while an optional combustion or devolatization facility may be close to the processing facility, it may also be at a remote location. Production of RDF may involve the following steps: preliminary liberation, size screening, magnetic separation, coarse shredding, and refining separation. The residual material may be sold in its processed form or it may be compressed into pellets, bricks or logs and used for other purposes either stand-alone or in a recursive recycling process. Advanced RDF processing methods, for example pressurized steam treatment in an autoclave, may remove or significantly reduce harmful pollutants and heavy metals.

Usually, the RDF is available in large pellets such as 1 inch diameter and 3-4 inches long. The RDF pellets in line 102 may be reduced in size in the pretreatment section 110 to ensure better handling and proper melting in the reactor.

In the pretreatment section 110, the mixed-plastic stream in line 102 is received with minimal sorting and cleaning. Waste material is separated from the plastic feed stream and discharged in line 114 from the pretreatment section 110. Contaminants are also removed from the mixed-plastic stream which may be discharged in line 114 from the pretreatment section 110. Also, the non-plastic material may be separated from the plastic feed stream and taken in line 114 from the pretreatment section 110. A plastic feed stream is discharged in line 112 from the pretreatment section 110 and fed to a pyrolysis reactor 120. The plastic feed stream in line 112 may comprise compressed plastic articles separated from a bail of compacted plastic articles.

As used herein, “waste material”, “contaminant” and “non-plastic material” may include any item or object, including but not limited to, metals (ferrous and nonferrous), metal alloys, rubber, foam, glass (including, but not limited to borosilicate or soda lime glass, and various colored glass), ceramics, paper, cardboard, Teflon, PE, bundled wires, insulation covered wires, rare earth elements, leaves, wood, plants, parts of plants, textiles, bio-waste, packaging, electronic waste, batteries and accumulators, end-of-life vehicles, mining, construction, and demolition waste, crop wastes, forest residues, purpose-grown grasses, woody energy crops, microalgae, urban food waste, food waste, hazardous chemical and biomedical wastes, construction debris, farm wastes, biogenic items, non-biogenic items, objects with a specific carbon content, and any other objects that may be found within municipal solid waste.

The plastic feed stream in line 112 may be pyrolyzed in the first pyrolysis reactor 120 to produce a pyrolysis vapor stream. In an aspect, the plastic material in the plastic feed stream in line 112 may include chopped plastic chips or particles. An augur or an elevated hopper may be used to transport the plastic feed as whole articles or as chips into the pyrolysis reactor. Plastic articles or chips may be heated to above the plastic melting point into a melt and injected or augured into the pyrolysis reactor. An augur may operate in such a way as to move whole plastic articles into the pyrolysis reactor and simultaneously melt the plastic articles in the augur by friction or by indirect heat exchange into a melt which enters the reactor in a molten state.

In an aspect, the first pyrolysis reactor 120 may include a rotary reactor. In the rotary reactor 120, the plastic feed stream in line 112 is pyrolyzed and converted to smaller hydrocarbon molecules which vaporize at pyrolysis conditions to provide pyrolysis vapor. At these conditions, a solid char is also produced. In the rotary reactor 120, the plastic feed stream in line 112 is heated to a temperature of about 450° C. (842° F.) to about 700° C. (1292° F.).

A pyrolysis vapor stream may be discharged from a top of the rotary reactor 120 in a pyrolysis vapor line 122 extending from a top of the rotary reactor 120 and a char stream may be discharged from the rotary reactor 120 in a char line 124. The char line 124 may extend from a bottom of the rotary reactor 120. The atmosphere in the rotary reactor 120 is inert, which is preferably an oxygen-free, nitrogen atmosphere, but may be any other inert non-oxidizing atmosphere or under vacuum. Pressure in the rotary reactor 120 may be about atmospheric pressure of about −5 kPa (gauge) (−0.6 psig) to about 5 kPa (gauge) (0.6 psig) and preferably about −3 kPa (gauge) (−0.36 psig) to about 3 kPa (gauge) (0.36 psig). Pyrolysis conditions may be maintained for a sufficient residence time to produce a dried char product and a pyrolysis vapor stream at the outlet end of the rotary reactor 120. Dried char may be disposed of, used as fuel, or further processed for other purposes.

In an exemplary embodiment the first pyrolysis reactor 120 may be a rotary calciner. A rotary calciner has an elongated, horizontal shell which may have a greater length than its height. The shell may generally have a cylindrical configuration. The rotary calciner 120 may comprise a rotary kiln, a fired kiln, a fired rotary kiln or other substantially similar equipment. All fired kilns may be indirectly fired. The shell may be slightly inclined downwardly from the inlet end to the outlet end. Circumferential rotation of the shell and gravity operate to move the plastic feed stream in line 112 from the inlet end to the outlet end enabling the plastic material to pyrolyze and faster vaporization of pyrolyzed material from the char. Baffles may be located on an inner surface of the shell or otherwise supported to propel material toward the outlet end. The rotary calciner 120 may have rotating equipment that mechanically moves the plastic feed stream in line 112 from the inlet end to the outlet end under heating.

The rotary reactor 120 operates to crack polymer to lighter hydrocarbons such as ethylene and propylene which vaporize and may go up in the pyrolysis vapor line 122. The pyrolysis vapor stream is discharged from the rotary reactor 120 in line 122.

In an embodiment, the pyrolysis vapor stream in line 122 is pyrolyzed in a second pyrolysis reactor 130 to produce a pyrolysis product stream. The second pyrolysis reactor 130 may include a tank reactor. In an aspect, the pyrolysis vapor stream in line 122 may be condensed in a condenser before charging it to the second pyrolysis reactor 130.

The second pyrolysis reactor 130 may be operated at a lower temperature than the first pyrolysis reactor 120. In an embodiment, the second pyrolysis reactor 130 may include a low-temperature pyrolysis reactor (LTPR).

In an exemplary embodiment, the tank reactor 130 may be a continuous stirred tank reactor (CSTR). The tank reactor 130 may employ an agitator. In the tank reactor 130, the pyrolysis vapor stream is heated and pyrolyzed into a pyrolysis product stream. The tank reactor 130 provides enough residence time for the pyrolysis vapor stream to convert to low-temperature pyrolysis products. The tank reactor 130 may operate at a temperature from about 300° C. (572° F.) to about 600° C. (1112° F.), or preferably about 380° C. (716° F.) to about 450° C. (842° F.), a pressure from about 0.069 MPa (gauge) (10 psig) to about 1.38 MPa (gauge) (200 psig), or preferably about 0.138 MPa (gauge) (20 psig) to about 0.55 MPa (gauge) (80 psig), a liquid hourly space velocity of the plastic feed from about 0.1 hr⁻¹ to about 2 hr⁻¹, or preferably from about 0.2 hr⁻¹ to about 0.5 hr⁻¹. A nitrogen blanket or a dedicated nitrogen sweeping stream in line 123 may optionally be added to the tank reactor 130 at a rate of about 17 Nm³/m³ (100 scf/bbl) to about 850 Nm³/m³ plastic feed (5,000 scf/bbl), or more preferably about 170 Nm³/m³ (1000 scf/bbl) to about 340 Nm³/m³ plastic feed (2000 scf/bbl). The nitrogen sweeping stream in line 123 serves as a dilution gas to reduce impure gas partial pressure in the total vapor product.

In an embodiment, the pyrolysis vapor stream in line 122 may be pyrolyzed in the presence of a catalyst in the tank reactor 130 to produce the pyrolysis product stream. The tank reactor 130 comprises a suitable catalyst such as ZSM-type zeolite catalyst.

The tank reactor 130 contains liquid in phase equilibrium with the vapor product stream. A pyrolysis product stream may be withdrawn from the tank reactor 130 in line 132. A solids rich product stream may be withdrawn from the bottom of the tank reactor 130 in line 134. The solids rich product stream may comprise char and non-organics. The solids rich product stream in line 134 may comprise unreacted polymer oil and char. The polymer oil has yet to be pyrolyzed or converted to pyrolysis oil. In an aspect, the polymer oil in the solids rich product stream in line 134 may comprise C31+ hydrocarbons. The polymer oil in the solids rich product stream in line 134 may be further pyrolyzed to increase conversion efficiency in the process. In an embodiment, the solids rich product stream in line 134 may be recycled to the rotary reactor 134.

Convective heat transfer inside tank reactor 130 along with mixing provides uniform heating, an advantage over pyrolysis reaction methods heated via external indirect heating, commonly seen in augur or rotary kiln reactors.

The pyrolysis product stream in line 132 comprises a range of hydrocarbons optionally carried by a nitrogen stream. The pyrolysis product stream in line 132 may comprise pyrolysis oil. In an embodiment, the pyrolysis product stream in line 132 may be hydrotreated in a post hydrotreating reactor 140 to produce a hydrotreated pyrolysis product stream.

Hydrotreating is a process wherein hydrogen is contacted with hydrocarbon in the presence of hydrotreating catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds may be saturated. Aromatics may also be saturated. Some hydrotreating processes are specifically designed to saturate aromatics.

A hydrotreating hydrogen stream in line 135 is passed to the post hydrotreating reactor 140. In the post hydrotreating reactor 140, the pyrolysis product stream in line 132 may be contacted with a hydrotreating catalyst under hydrotreating conditions in the presence of hydrogen to produce a hydrotreated pyrolysis product stream. The post hydrotreating reactor 140 may hydrotreat the pyrolysis product stream in line 132 over a hydrotreating catalyst to reduce the boiling range of the components present in the pyrolysis product stream.

Suitable hydrotreating catalysts for use in the post hydrotreating reactor 140 may include any known conventional hydrotreating catalysts and include those which are comprised of at least one Group VIII metal, preferably iron, cobalt and nickel, more preferably cobalt and/or nickel and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. In the high sulfur and nitrogen environment of the post hydrotreating reactor 140, noble metal catalysts may be discouraged. More than one type of hydrotreating catalyst may be used in the post hydrotreating reactor 140. The Group VIII metal is typically present in an amount ranging from about 2 to about 20 wt %, preferably from about 4 to about 12 wt %. The Group VI metal will typically be present in an amount ranging from about 1 to about 25 wt %, preferably from about 2 to about 25 wt %.

Hydrotreating conditions in the post hydrotreating reactor 140 may include a temperature from about 290° C. (550° F.) to about 455° C. (850° F.), suitably 316° C. (600° F.) to about 427° C. (800° F.) and preferably 343° C. (650° F.) to about 399° C. (750° F.), a pressure from about 2.1 MPa (gauge) (300 psig), preferably 4.1 MPa (gauge) (600 psig) to about 20.6 MPa (gauge) (3000 psig), suitably 13.8 MPa (gauge) (2000 psig), preferably 12.4 MPa (gauge) (1800 psig), a liquid hourly space velocity of the feed from about 0.1 hr⁻¹, suitably 0.5 hr⁻¹, to about 10 hr⁻¹ preferably from about 1.5 to about 8.5 hr⁻¹, and a hydrogen rate of about 168 Nm³/m³ (1,000 scf/bbl), to about 1,011 Nm³/m³ oil (6,000 scf/bbl), preferably about 168 Nm³/m³ oil (1,000 scf/bbl) to about 674 Nm³/m³ oil (4,000 scf/bbl), with a hydrotreating catalyst or a combination of hydrotreating catalysts. A hydrotreated pyrolysis oil stream is discharged in line 142 from the post hydrotreating reactor 140.

In the embodiment as shown in FIG. 1, a lower investment sortation system may be utilized in the pretreatment section 110 to create a high-contaminant feedstock. Since the feedstock is more contaminated, a rotary reactor 120 such as a rotary calciner is used as the first stage pyrolysis reactor. This type of reactor is better able to handle increased solids from the feed contaminants. The vapors from the rotary calciner 120 are sent to the tank reactor 130 such as a CSTR as the second stage pyrolysis reactor. Since the rotary calciner would operate at a high temperature, the feedstock to the CSTR reactor will have a higher concentration of high boiling range material. The CSTR would continue the pyrolysis of this stream to generate lower boiling range product. The catalyst may be added in the CSTR reactor to facilitate the conversion. Any char formed in the CSTR is recycled to the rotary calciner 120. The pyrolysis oil product would then pass through the post hydrotreating reactor 140. Since the pyrolysis feed contained higher contaminants, it is expected that the pyrolysis oil would have higher contaminants. Therefore, hydrotreating severity in the post hydrotreating reactor 140 would likely increase. The cost for the higher severity hydrotreating should be less than the savings in the pretreatment capital required for the pre-treatment section 110.

Since the pyrolysis vapor stream in line 122 is produced from the rotary reactor 120, the pyrolysis vapor stream in line 122 may comprise heavier component and contaminants. The pyrolysis vapor stream in line 122 may be hydroprocessed before passing it to the tank reactor 130. In an alternate embodiment, a portion or an entirety of the pyrolysis vapor stream in line 122 may be taken from the rotary reactor 120 in line 148 through an open valve and hydrotreated in a hydrotreating reactor 150 in the presence of a hydrotreating catalyst to produce a hydrotreated pyrolysis stream. A hydrotreating hydrogen stream in line 149 is passed to the hydrotreating reactor 150 through an open control valve. The hydrotreating reactor 150 may include one or more hydrotreating catalysts as earlier described. The hydrotreating reactor 150 may be operated at similar hydrotreating conditions as described in FIG. 1.

The hydrotreating reactor 150 may be operated at include a temperature from about 290° C. (550° F.) to about 455° C. (850° F.), suitably 316° C. (600° F.) to about 427° C. (800° F.) and preferably 343° C. (650° F.) to about 399° C. (750° F.), a pressure from about 2.1 MPa (gauge) (300 psig), preferably 4.1 MPa (gauge) (600 psig) to about 20.6 MPa (gauge) (3000 psig), suitably 13.8 MPa (gauge) (2000 psig), preferably 12.4 MPa (gauge) (1800 psig), a liquid hourly space velocity of the feed from about 0.1 hr⁻¹, suitably 0.5 hr⁻¹, to about 10 hr⁻¹, preferably from about 1.5 to about 8.5 hr⁻¹, and a hydrogen rate of about 168 Nm³/m³ (1,000 scf/bbl), to about 1,011 Nm³/m³ oil (6,000 scf/bbl), preferably about 168 Nm³/m³ oil (1,000 scf/bbl) to about 674 Nm³/m³ oil (4,000 scf/bbl), with a hydrotreating catalyst or a combination of hydrotreating catalysts.

The hydrotreated pyrolysis stream is discharged in line 152 from the hydrotreating reactor 150. The hydrotreated pyrolysis stream in line 152 may comprise fewer heavier components than the pyrolysis vapor stream in line 122. A portion or an entirety of the hydrotreated pyrolysis stream may be taken in line 154 from the hydrotreating reactor 150 in the hydrotreated pyrolysis stream in line 152 and charged through an open control valve to the tank reactor 130. The hydrotreated pyrolysis stream in line 154 may be pyrolyzed in the tank reactor 130. A hydrotreated product stream may be taken from the hydrotreated pyrolysis stream in line 152.

The hydrotreating reactor 150 may be optionally used and the pyrolysis vapor stream in line 122 may be directly pyrolyzed in the tank reactor 130. In the embodiment where the pyrolysis vapor stream in line 122 is directly pyrolyzed in the tank reactor 130, the heavier components and contaminants may be removed in the post hydrotreating reactor 140.

FIG. 2 shows another embodiment 201 of the process for converting plastics. In the embodiment as shown in FIG. 2, the mixed plastic stream is separated to provide a high-contaminant plastic feed stream and a low-contaminant plastic feed stream. These feed streams are pyrolyzed in suitable reactors based on the contaminant level in these streams.

As shown in FIG. 2, the mixed-plastic may be taken in a first mixed-plastic stream in line 202, a second mixed-plastic stream in line 204, and a third mixed-plastic stream in line 206. The first mixed-plastic stream in line 202, the second mixed-plastic stream in line 204, and the third mixed-plastic stream in line 206 are charged to the pre-treatment section 210. The pre-treatment section may be a similar to pre-treatment section as described in FIG. 1. The first mixed-plastic stream in line 202, the second mixed-plastic stream in line 204, and the third mixed-plastic stream in line 206 may be taken from various sources as described earlier in FIG. 1.

In the pre-treatment section 210, the mixed-plastic streams are sorted to provide a high-contaminant plastic feed stream and a low-contaminant plastic feed stream. The high-contaminant plastic feed stream is discharged in line 212 from the pre-treatment section 210. The low-contaminant plastic feed stream may be discharged in line 214 from the pre-treatment section 210. The high-contaminant plastic feed stream in line 212 may comprise about 10 wt % to about 50 wt % non-desired plastic. Non-limiting examples of the non-desired plastic may include polycarbonates, polylactic acid, acrylonitrile butadiene styrene, acrylic, melamine, and nylon. The low-contaminant plastic feed stream in line 214 may comprise less than about 10 wt % non-desired plastic.

Waste material is separated from the mixed-plastic streams and discharged in line 218 from the pretreatment section 210. Contaminants are also removed from the mixed-plastic stream which may be discharged in line 218 from the pre-treatment section 210. Also, the non-plastic material may be separated from the mixed-plastic stream and taken in line 218 from the pretreatment section 210. The “waste material”, “contaminant” and “non-plastic material” are as earlier defined with regard to FIG. 1.

Further, polyethylene terephthalate (PET) material such as PET bottles may also be separated from the mixed-plastic streams in the pretreatment section 210. A PET material stream is discharged in line 216 from the pre-treatment section 210.

The high-contaminant plastic feed stream in line 212 may be pyrolyzed in a first pyrolysis reactor 220 to produce a pyrolysis vapor stream. In an aspect, the first pyrolysis reactor 220 may include a rotary reactor. In the rotary reactor 220, the high-contaminant plastic feed stream in line 212 is pyrolyzed and converted to smaller hydrocarbon molecules which vaporize at pyrolysis conditions to provide pyrolysis vapor. The rotary reactor 220 may be operated at similar operating conditions as described earlier in FIG. 1. The solid char may be removed in line 224 from the rotary reactor 220. In an exemplary embodiment the first pyrolysis reactor 220 may be a rotary calciner.

The rotary reactor 220 operates to crack polymer to lighter hydrocarbons such as ethylene and propylene which vaporize and may go up in the pyrolysis vapor line 222. The pyrolysis vapor stream is discharged from the rotary reactor 220 in line 222. The pyrolysis product stream in line 222 may comprise pyrolysis oil.

The low-contaminant plastic feed stream in line 214 may be pyrolyzed in a second pyrolysis reactor 230. The second pyrolysis reactor 230 may be operated at a lower temperature than the first pyrolysis reactor 220. In an embodiment, the second pyrolysis reactor 230 may include a tank reactor 230. A nitrogen blanket or a dedicated nitrogen sweeping stream in line 223 may optionally be added to the tank reactor 230. The tank reactor 230 may be similar to and operated at similar conditions as earlier described in FIG. 1.

A pyrolysis product stream may be withdrawn from the tank reactor 230 in line 232. The pyrolysis product stream in line 232 may comprise pyrolysis oil. In an embodiment, the pyrolysis product stream in line 232 may be hydrotreated in a post hydrotreating reactor 260 to produce a hydrotreated pyrolysis product stream.

A hydrotreating hydrogen stream in line 235 is passed to the post hydrotreating reactor 260. In the post hydrotreating reactor 260, the pyrolysis product stream in line 232 may be contacted with a hydrotreating catalyst under hydrotreating conditions in the presence of hydrogen to produce a hydrotreated pyrolysis product stream. The post hydrotreating reactor 260 may hydrotreat the pyrolysis product stream in line 232 over a hydrotreating catalyst to reduce the boiling range of the components present in the pyrolysis product stream. The post hydrotreating reactor 260 may include one or more hydrotreating catalysts as previously described in FIG. 1. The post hydrotreating reactor 260 may be operated at similar hydrotreating conditions as earlier described in FIG. 1. A hydrotreated pyrolysis oil stream is discharged in line 262 from the post hydrotreating reactor 140.

Since the pyrolysis vapor stream in line 222 is produced from the high-contaminant feed stream in the rotary reactor 220, the pyrolysis vapor stream in line 222 may comprise heavier component and contaminants. The pyrolysis vapor stream in line 222 may be hydroprocessed to lower the boiling range of the components. A portion or an entirety of the pyrolysis vapor stream in line 222 may be taken from the rotary reactor 220 in line 226 through an open control valve thereon and hydrotreated in a hydrotreating reactor 250 in the presence of a hydrotreating catalyst to produce a hydrotreated pyrolysis stream. A hydrotreating hydrogen stream in line 249 is passed to the hydrotreating reactor 250. The hydrotreating reactor 250 may include one or more hydrotreating catalysts as earlier described. The hydrotreated pyrolysis stream is discharged in line 252 from the hydrotreating reactor 250.

A portion or an entirety of the hydrotreated pyrolysis stream may be taken in line 254 from the hydrotreating reactor 250 in line 252 and charged though an open control valve to the tank reactor 230. The hydrotreated pyrolysis stream in line 254 may be pyrolyzed in the tank reactor 230.

The hydrotreating reactor 250 may be optionally used. In the embodiment with optional hydrotreating reactor 250, the pyrolysis vapor stream in line 222 may be taken as pyrolysis oil or it can be further pyrolyzed in the tank reactor 230. Further, in the embodiment with optional hydrotreating reactor 250, the heavier component and contaminants may be removed in the post hydrotreating reactor 260.

Referring back to the pre-treatment section 210, the PET material stream in line 216 may be charged to a PET processing unit 240. In an exemplary embodiment, the PET processing unit 240 is a PET solvolysis unit. In the PET solvolysis unit 240, PET from the PET material stream in line 216 is depolymerized into monomers. In the PET solvolysis unit 240, PET may be depolymerized into monomers by using any one or more of the three methods, i.e., a hydrolysis method using water as a solvent, an alcoholysis method using an alcohol as a solvent and a glycolysis method using a glycol as a solvent.

The hydrolysis method is, for example, a method wherein a polyethylene terephthalate melt is allowed to react with water vapors and then allowed to react with ammonium hydroxide to decompose polyethylene terephthalate into terephthalic acid and ethylene glycol. Although this method has an advantage that a glycol or an alcohol does not need to be used for the reaction, it is necessary to use a pressure-resistant special apparatus because the reaction is carried out under the condition of high pressure.

The alcoholysis method is, for example, a method wherein a polyester is heated in an alcohol solvent, if necessary, a catalyst is added, to depolymerize the polyester. This method has an advantage that when PET is depolymerized using, for example, methanol as a solvent, dimethyl terephthalate, a useful and easy-handled monomer, is directly formed by the depolymerization reaction and the depolymerization reaction proceeds relatively rapidly. On the other hand, the alcohol used as a solvent is low-boiling, and in order to promote the reaction, application of pressure is necessary. As such, the reaction is carried out in methanol in a supercritical or subcritical state, so that a pressure-resistant special apparatus is necessary.

The glycolysis method is a method wherein a polyester is heated together with a depolymerization catalyst such as sodium carbonate in an excess alkylene glycol solvent to depolymerize the polyester and thereby form a bis(β-hydroxyalkyl) terephthalate and ethylene glycol. For example, when ethylene glycol is used as a solvent, bis(β-hydroxyethyl) terephthalate is formed by the depolymerization reaction, and by further adding methanol in the presence of a transesterification catalyst to perform transesterification, dimethyl terephthalate can be recovered.

From the PET solvolysis unit 240, a PET monomer stream is discharged in line 242.

In the embodiment as shown in FIG. 2, the mixed-plastic streams are separated into multiple feedstock types with different plastic compositions and contaminant levels. These different streams from the pre-treatment section 210 are then sent to different reactor configurations to optimize the conversion of each of the feedstock types. For example, the high-contaminant plastic feed stream is charged to the rotary reactor 220 that better handles the char byproducts. The low-contaminant plastic feed stream is fed to the tank reactor 230 that could optimize the yields. The PET waste material is converted to monomers in the PET solvolysis unit 240. This sorting and dedicated processing of the waste plastic streams maximize the raw feedstock utilization into recycled plastics and minimizes the waste from the pre-treatment section 210.

Example

A 100 kg of polymeric feed was used. The composition with types of polymer in the feed is provided in Table 1 below:

TABLE 1
Feed composition

	Polymer type	Mass (kg)

	Polyethylene (PE)	34
	Polypropylene (PP)	12
	Polyethylene terephthalate (PET)	32
	Poly vinyl chloride (PVC)	8
	Paper	5
	Ash	6
	Other	3
	Total	100

The feed was processed in the two reactors. First the feed was pyrolyzed in the first pyrolysis reactor which was rotary kiln. The products from the rotary kiln include the 150° C.-380° C. distillate and the 380° C.₊ Heavy VGO. This product from the rotary kiln was then pyrolyzed in the CSTR. The parameters and the results are summarized in Table 2 below:

	TABLE 2
		Step 2
	Step 1 Pyrolysis	Pyrolysis

Reactor type

Rotary kiln

Product

CSTR

Temperature

470° C.

380° C.

Pressure

	1 psig in			Total
	vacuum		5 psig	yield
	Mass		Mass	from two
Product boiling range	yield	Mass	yield	steps

C4− gas	3		5	8
C5+ −150° C. naphtha	8		26	34
150° C.-380° C.	18	18	23	23
distillate
380° C.+ Heavy VGO	41	41	2	2
and residual oil
Solid with ash and char	30		3	33
Total (kg)	100	59	59	100

About 60% of useable fuels were produced by the process.

Specific Embodiments

While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

A first embodiment of the present disclosure is a process for converting plastics, comprising pyrolyzing a plastic feed stream in a first pyrolysis reactor to produce a pyrolysis vapor stream; and pyrolyzing the pyrolysis vapor stream in a second pyrolysis reactor to produce a pyrolysis product stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the first pyrolysis reactor is a rotary reactor and the second pyrolysis reactor is a tank reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the pyrolysis vapor stream is pyrolyzed in the presence of a catalyst in the second pyrolysis reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising hydrotreating the pyrolysis vapor stream in a hydrotreating reactor in the presence of a hydrotreating catalyst to produce a hydrotreated pyrolysis stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising passing a mixed-plastic stream to a pretreatment section to separate waste material from the plastic; and taking the plastic feed stream from the pretreatment section. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising separating a high-contaminant plastic feed stream from the mixed-plastic stream in the pretreatment section, the high-contaminant plastic feed stream comprising about 10 wt % to about 50 wt % non-desired plastic; and charging the high-contaminant plastic feed stream to the first pyrolysis reactor to produce the pyrolysis vapor stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising separating a low-contaminant plastic feed stream from the mixed-plastic stream in the pretreatment section, the low-contaminant plastic feed stream comprising less than about 10 wt % non-desired plastic; and charging the low-contaminant plastic feed stream to the second pyrolysis reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the non-desired plastic includes polycarbonates, polylactic acid, acrylonitrile butadiene styrene, acrylic, melamine, and nylon. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the contaminant includes non-plastic material. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising discharging a char stream from the first pyrolysis reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the first pyrolysis reactor is operated at a higher temperature than the second pyrolysis reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising taking a recycle stream comprising char from the second pyrolysis reactor; and recycling the recycle stream comprising char to the first pyrolysis reactor.

A second embodiment of the present disclosure is a process for converting plastics, comprising separating a plastic feed stream from a mixed-plastic stream in a pretreatment section, the mixed-plastic stream comprising more than 10 wt % non-desired plastic; pyrolyzing the plastic feed stream in a first pyrolysis reactor to produce a pyrolysis vapor stream; and pyrolyzing the pyrolysis vapor stream in a second pyrolysis reactor to produce a pyrolysis product stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the first pyrolysis reactor is a rotary reactor and the second pyrolysis reactor is a tank reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising separating a high-contaminant plastic feed stream from the mixed-plastic stream in the pretreatment section, the high-contaminant plastic feed stream comprising about 10 wt % to about 50 wt % non-desired plastic; and charging the high-contaminant plastic feed stream to the first pyrolysis reactor to produce the pyrolysis vapor stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising separating a low-contaminant plastic feed stream from the mixed-plastic stream in the pretreatment section, the low-contaminant plastic feed stream comprises less than about 10 wt % non-desired plastic; and charging the low-contaminant plastic feed stream to the second pyrolysis reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the first pyrolysis reactor is operated at a higher temperature than the second pyrolysis reactor.

A third embodiment of the present disclosure is a process for converting plastics, comprising pyrolyzing a plastic feed stream in a rotary pyrolysis reactor to produce a pyrolysis vapor stream, wherein the plastic feed stream is separated from a mixed-plastic stream; and pyrolyzing the pyrolysis vapor stream in a second pyrolysis reactor to produce a pyrolysis product stream, wherein the second pyrolysis reactor is operating at a lower temperature than the rotary pyrolysis reactor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising separating a high-contaminant plastic feed stream from the mixed-plastic stream, the high-contaminant plastic feed stream comprising about 10 wt % to about 50 wt % non-desired plastic; and charging the high-contaminant plastic feed stream to the rotary pyrolysis reactor to produce the pyrolysis vapor stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising separating a low-contaminant plastic feed stream from the mixed-plastic stream, the low-contaminant plastic feed stream comprising less than about 10 wt % non-desired plastic; and charging the low-contaminant plastic feed stream to the second pyrolysis reactor.

Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present disclosure to its fullest extent and easily ascertain the essential characteristics of this disclosure, without departing from the spirit and scope thereof, to make various changes and modifications of the disclosure and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.